Golf ball

ABSTRACT

A golf ball  14  has a northern hemisphere N above an equatorial line Eq and a southern hemisphere S below the equatorial line Eq. Each of the northern hemisphere N and the southern hemisphere S has a pole vicinity region  30,  an equator vicinity region  32,  and a mid region  34.  Each of the pole vicinity region  30,  the equator vicinity region  32,  and the mid region  34  has numerous dimples  20.  The dimple pattern of the pole vicinity region  30  includes four units that are rotationally symmetrical to each other about a pole P. The dimple pattern of the equator vicinity region  32  includes six units that are rotationally symmetrical to each other about the pole P. The dimples  20  included in the mid region  34  are arranged along a mid latitude line  28.  The number of the dimples  20  included in the mid region  34  is 24.

This application claims priority on Patent Application No. 2009-15149 filed in JAPAN on Jan. 27, 2009. The entire contents of this Japanese Patent Application are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to golf balls. Specifically, the present invention relates to improvement of dimples of golf balls.

2. Description of the Related Art

Golf balls have a large number of dimples on the surface thereof. The dimples disturb the air flow around the golf ball during flight to cause turbulent flow separation. By causing the turbulent flow separation, separation points of the air from the golf ball shift backwards leading to a reduction of drag. The turbulent flow separation promotes the displacement between the separation point on the upper side and the separation point on the lower side of the golf ball, which results from the backspin, thereby enhancing the lift force that acts upon the golf ball. The reduction of drag and the enhancement of lift force are referred to as a “dimple effect”. Excellent dimples efficiently disturb the air flow. The excellent dimples produce a long flight distance.

There have been various proposals for a dimple pattern. JPH4-109968 discloses a golf ball whose hemisphere is divided into six units. These units have dimple patterns that are equivalent to each other. US2004/157682 (JP2004-243124) discloses a dimple pattern in which an octahedron is used for dividing a region near a pole and an icosahedron is used for dividing a region near an equatorial line.

The present inventor has proposed a golf ball having an improved dimple pattern in US2007/149321 (JP2007-175267). The golf ball is shown in FIGS. 11 to 14. The golf ball 2 has a northern hemisphere N and a southern hemisphere S. Each hemisphere has a pole vicinity region 4, an equator vicinity region 6, and a coordination region 8. The number of units Up of the pole vicinity region 4 is different from the number of units Ue of the equator vicinity region 6. This difference disturbs air flow. The difference between the characteristic of the pole vicinity region 4 and the characteristic of the equator vicinity region 6 is alleviated by the coordination region 8.

In the golf ball 2 disclosed in US2007/149321 (JP2007-175267), the alleviation of the difference between the characteristic of the pole vicinity region 4 and the characteristic of the equator vicinity region 6 due to the coordination region 8 is not sufficient. In the golf ball 2, dimples 10 are unevenly located in the coordination region 8. Due to this uneven location, a land having a large area occurs. This land impairs the dimple effect.

The greatest interest to golf players concerning golf balls is flight distance. In light of flight performance, there is room for improvement in the dimple pattern. An objective of the present invention is to provide a golf ball having excellent flight performance.

SUMMARY OF THE INVENTION

The surface of a golf ball according to the present invention can be divided into a northern hemisphere and a southern hemisphere. Each of the northern hemisphere and the southern hemisphere has a pole vicinity region, an equator vicinity region, and a mid region located between the pole vicinity region and the equator vicinity region. Each of the pole vicinity region, the equator vicinity region, and the mid region has a large number of dimples. A dimple pattern of the pole vicinity region includes a plurality of units that are rotationally symmetrical to each other about a pole. A dimple pattern of the equator vicinity region includes a plurality of units that are rotationally symmetrical to each other about the pole. The number Np of the units of the pole vicinity region is different from the number Ne of the units of the equator vicinity region. The dimples included in the mid region are arranged substantially along a latitude line.

In the golf ball, because the number of the units of the pole vicinity region is different from the number of the units of the equator vicinity region, a superior dimple effect is achieved. In the golf ball, the mid region suppresses uneven location of the dimples. The golf ball has excellent flight performance.

Preferably, the latitude line has a latitude of 20° or greater and 40° or less. Preferably, the latitude of the latitude line is substantially 30°.

Preferably, the number Np is equal to or greater than 3 and equal to or less than 6, and the number Ne is equal to or greater than 3 and equal to or less than 6.

Preferably, the number Nm of the dimples in the mid region is equal to or greater than 18 and equal to or less than 48. Preferably, the number Nm is a common multiple of the number Np and the number Ne.

Preferably, the dimples included in the mid region have the same diameter, and these dimples are arranged along the latitude line at regular intervals. Preferably, a central angle between dimples adjacent to each other is equal to or greater than 7.5° and equal to or less than 20°.

Preferably, the number of dimples that are adjacent to a boundary line between the pole vicinity region and the mid region and included in the pole vicinity region is equal to the number of the dimples that are arranged along the latitude line. Preferably, the number of dimples that are adjacent to a boundary line between the equator vicinity region and the mid region and included in the equator vicinity region is equal to the number of the dimples that are arranged along the latitude line.

Preferably, a ratio of the number of the dimples that exist in the pole vicinity region to the number of the dimples that exist in each hemisphere is equal to or greater than 20% and equal to or less than 70%. Preferably, a ratio of the number of the dimples that exist in the equator vicinity region to the number of the dimples that exist in each hemisphere is equal to or greater than 20% and equal to or less than 70%.

Preferably, a dimple pattern of the northern hemisphere is equivalent to a dimple pattern of the southern hemisphere.

Preferably, the total number of the dimples is equal to or greater than 200 and equal to or less than 600. Preferably, each dimple has a diameter of 2.00 mm or greater and 6.00 mm or less. Preferably, a ratio of the sum of areas of all the dimples to a surface area of a phantom sphere is equal to or greater than 60% and equal to or less than 88%. Preferably, the total volume of the dimples is equal to or greater than 250 mm³ and equal to or less than 400 mm³. Preferably, each dimple has a depth of 0.05 mm or greater and 0.60 mm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a golf ball according to an embodiment of the present invention;

FIG. 2 is an enlarged front view of the golf ball in FIG. 1;

FIG. 3 is a plan view of the golf ball in FIG. 2;

FIG. 4 is a plan view of the golf ball in FIG. 2;

FIG. 5 is a plan view of the golf ball in FIG. 2;

FIG. 6 is a partially enlarged cross-sectional view of the golf ball in FIG. 1;

FIG. 7 is a front view of a golf ball according to Comparative Example 1;

FIG. 8 is a plan view of the golf ball in FIG. 7;

FIG. 9 is a front view of a golf ball according to Comparative Example 2;

FIG. 10 is a plan view of the golf ball in FIG. 9;

FIG. 11 is a front view of a golf ball according to Comparative Example 3;

FIG. 12 is a plan view of the golf ball in FIG. 11;

FIG. 13 is a plan view of the golf ball in FIG. 11; and

FIG. 14 is a plan view of the golf ball in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe in detail the present invention based on preferred embodiments with reference to the accompanying drawings.

A golf ball 14 shown in FIG. 1 includes a spherical core 16 and a cover 18. On the surface of the cover 18, a large number of dimples 20 are formed. Of the surface of the golf ball 14, a part other than the dimples 20 is a land 22. The golf ball 14 includes a paint layer and a mark layer on the external side of the cover 18 although these layers are not shown in the drawing. A mid layer may be provided between the core 16 and the cover 18.

The golf ball 14 has a diameter of 40 mm or greater and 45 mm or less. From the standpoint of conformity to the rules established by the United States Golf Association (USGA), the diameter is more preferably equal to or greater than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm and particularly preferably equal to or less than 42.80 mm. The golf ball 14 has a weight of 40 g or greater and 50 g or less. In light of attainment of great inertia, the weight is more preferably equal to or greater than 44 g and particularly preferably equal to or greater than 45.00 g. From the standpoint of conformity to the rules established by the USGA, the weight is more preferably equal to or less than 45.93 g.

The core 16 is formed by crosslinking a rubber composition. Examples of base rubbers for use in the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. Two or more types of these rubbers may be used in combination. In light of resilience performance, polybutadienes are preferred, and in particular, high-cis polybutadienes are preferred.

In order to crosslink the core 16, a co-crosslinking agent is suitably used. Examples of preferable co-crosslinking agents in light of resilience performance include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. Preferably, the rubber composition includes an organic peroxide together with a co-crosslinking agent. Examples of suitable organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.

According to need, various additives such as a filler, sulfur, a vulcanization accelerator, a sulfur compound, an anti-aging agent, a coloring agent, a plasticizer, a dispersant, and the like are included in the rubber composition for the core 16 at an adequate amount. Crosslinked rubber powder or synthetic resin powder may be also included in the rubber composition.

The core 16 has a diameter of 30.0 mm or greater and particularly 38.0 mm or greater. The diameter of the core 16 is equal to or less than 42.0 mm and particularly equal to or less than 41.5 mm. The core 16 may be formed with two or more layers.

A suitable polymer for the cover 18 is an ionomer resin. Examples of preferable ionomer resins include binary copolymers formed with an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Examples of other preferable ionomer resins include ternary copolymers formed with: an α-olefin; an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and an α,β-unsaturated carboxylate ester having 2 to 22 carbon atoms. For the binary copolymer and the ternary copolymer, preferable α-olefins are ethylene and propylene, while preferable α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In the binary copolymer and the ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of metal ions for use in neutralization include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion, and neodymium ion.

Other polymers may be used for the cover 18 instead of an ionomer resin. Examples of the other polymers include polyurethanes, polystyrenes, polyamides, polyesters, and polyolefins. In light of spin performance and scuff resistance, polyurethanes are preferred. Two or more types of these polymers may be used in combination.

According to need, a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the cover 18 at an adequate amount. For the purpose of adjusting specific gravity, powder of a metal with a high specific gravity such as tungsten, molybdenum, and the like may be included in the cover 18.

The cover 18 has a thickness of 0.2 mm or greater and particularly 0.3 mm or greater. The thickness of the cover 18 is equal to or less than 2.5 mm and particularly equal to or less than 2.2 mm. The cover 18 has a specific gravity of 0.90 or greater and particularly 0.95 or greater. The specific gravity of the cover 18 is equal to or less than 1.10 and particularly equal to or less than 1.05. The cover 18 may be formed with two or more layers.

FIG. 2 is an enlarged front view of the golf ball 14 in FIG. 1. In FIG. 2, two poles P, two first latitude lines 24, two second latitude lines 26, two mid latitude lines 28, and an equatorial line Eq are depicted. The latitude of each pole P is 90°, and the latitude of the equatorial line Eq is 0°. The latitude of each first latitude line 24 is greater than the latitude of each second latitude line 26. The latitude of each mid latitude line 28 is less than the latitude of each first latitude line 24 and greater than the latitude of each second latitude line 26.

The golf ball 14 has a northern hemisphere N above the equatorial line Eq and a southern hemisphere S below the equatorial line Eq. Each of the northern hemisphere N and the southern hemisphere S has a pole vicinity region 30, an equator vicinity region 32, and a mid region 34. The first latitude line 24 is the boundary line between the pole vicinity region 30 and the mid region 34. The second latitude line 26 is the boundary line between the equator vicinity region 32 and the mid region 34. The pole vicinity region 30 is located between the pole P and the first latitude line 24. The equator vicinity region 32 is located between the second latitude line 26 and the equatorial line Eq. The mid region 34 is located between the first latitude line 24 and the second latitude line 26. In other words, the mid region 34 is located between the pole vicinity region 30 and the equator vicinity region 32.

Each of the pole vicinity region 30, the equator vicinity region 32, and the mid region 34 has a large number of dimples 20. As is clear from FIG. 2, all the dimples 20 have a circular plane shape. For each dimple 20 that intersects the first latitude line 24 or the second latitude line 26, the region to which the dimple 20 belongs is determined based on the center position of the dimple 20. The dimples 20 that intersect the first latitude line 24 and whose centers are located in the pole vicinity region 30 belong to the pole vicinity region 30. The dimples 20 that intersect the second latitude line 26 and whose centers are located in the equator vicinity region 32 belong to the equator vicinity region 32. The center of each dimple 20 is a point at which a straight line passing through the deepest part of the dimple 20 and the center of the golf ball 14 intersects the surface of a phantom sphere. The surface of the phantom sphere is the surface of the golf ball 14 when it is postulated that no dimple 20 exists.

FIGS. 3 to 5 are plan views of the golf ball 14 in FIG. 2. FIG. 3 shows four first longitude lines 36 together with the first latitude line 24 and the second latitude line 26. In FIG. 3, the region surrounded by the first latitude lines 24 is the pole vicinity region 30. The pole vicinity region 30 can be divided into four units Up. Each unit Up has a spherical triangular shape. The contour of each unit Up consists of the first latitude line 24 and two first longitude lines 36. In FIG. 3, for one unit Up, types of the dimples 20 are indicated by the reference letters A, B, D, E, F, and G. The pole vicinity region 30 has dimples A having a diameter of 5.00 mm; a dimple B having a diameter of 4.80 mm; dimples D having a diameter of 4.40 mm; dimples E having a diameter of 4.00 mm; dimples F having a diameter of 3.60 mm; and dimples G having a diameter of 3.00 mm.

The dimple patterns of the four units Up have 90° rotational symmetry. In other words, when the dimple pattern of one unit Up is rotated 90° in the latitude direction about the pole P, it substantially overlaps the dimple pattern of the adjacent unit Up. The state of “substantially overlapping” also includes the state in which the dimple 20 in one unit is shifted to some extent from the corresponding dimple 20 in another unit. The state of “being shifted to some extent” includes the state in which the center of the dimple 20 in one unit is deviated to some extent from the center of the corresponding dimple 20 in another unit. The distance between the center of the dimple 20 in one unit and the center of the corresponding dimple 20 in another unit is preferably equal to or less than 1.0 mm and more preferably equal to or less than 0.5 mm. Here, the state of “being shifted to some extent” includes the state in which the dimension of the dimple 20 in one unit is different to some extent from the dimension of the corresponding dimple 20 in another unit. The difference in dimension is preferably equal to or less than 0.5 mm and more preferably equal to or less than 0.3 mm. The dimension means the length of the longest line segment that can be depicted over the contour of the dimple 20. In the case of a circular dimple 20, the dimension is equal to the diameter of the dimple 20.

The dimple pattern of the pole vicinity region 30 can be also divided into two units. In this case, the dimple patterns of the units have 180° rotational symmetry. The dimple pattern of the pole vicinity region 30 has two rotational symmetry angles (i.e., 90° and 180°). The region having a plurality of rotational symmetry angles is divided into units Up based on the smallest rotational symmetry angle (90° in this case).

FIG. 4 shows six second longitude lines 38 together with the first latitude line 24 and the second latitude line 26. In FIG. 4, the outside of the second latitude line 26 is the equator vicinity region 32. The equator vicinity region 32 can be divided into six units Ue. Each unit Ue has a spherical trapezoidal shape. The contour of the unit Ue consists of the second latitude line 26, two second longitude lines 38, and the equatorial line Eq (see FIG. 2). In FIG. 4, for one unit Ue, types of the dimples 20 are indicated by the reference letters A, B, and D. The equator vicinity region 32 has the dimples A having a diameter of 5.00 mm; the dimples B having a diameter of 4.80 mm; and the dimples D having a diameter of 4.40 mm.

The dimple patterns of the six units Ue have 60° rotational symmetry. In other words, when the dimple pattern of one unit Ue is rotated 60° in the latitude direction about the pole P, it substantially overlaps the dimple pattern of the adjacent unit Ue. The dimple pattern of the equator vicinity region 32 can be also divided into three units. In this case, the dimple patterns of the units have 120° rotational symmetry. The dimple pattern of the equator vicinity region 32 can be also divided into two units. In this case, the dimple patterns of the units have 180° rotational symmetry. The dimple pattern of the equator vicinity region 32 has three rotational symmetry angles (i.e., 60°, 120°, and 180°). The region having a plurality of rotational symmetry angles is divided into units Ue based on the smallest rotational symmetry angle (60° in this case).

FIG. 5 shows the first latitude line 24 and the second latitude line 26. In FIG. 5, the region surrounded by the first latitude line 24 and the second latitude line 26 is the mid region 34. The mid region 34 has 24 dimples 20. As shown in FIG. 5, the mid region 34 has only dimples C. In other words, the dimples 20 included in the mid region 34 have the same diameter. The dimples C have a diameter of 4.70 mm.

As shown in FIG. 2, all the dimples 20 included in the mid region 34 are arranged along the mid latitude line 28. In other words, the latitudes of the dimples 20 included in the mid region 34 are the same as the latitude of the mid latitude line 28. The mid region 34 may have a dimple 20 whose latitude is different to some extent from the latitude of the mid latitude line 28. The difference between the latitude of this dimple 20 and the latitude of the mid latitude line 28 is preferably equal to or less than 5° and more preferably equal to or less than 2°.

In the golf ball 14, the number Np of the units Up of the pole vicinity region 30 is 4, while the number Ne of the units Ue of the equator vicinity region 32 is 6. These numbers are different from each other. The dimple pattern with the number Np and the number Ne being different from each other is varied. In the golf ball 14, air flow is efficiently disturbed during flight. The golf ball 14 has excellent flight performance. Examples of combinations of the number Np and the number Ne (Np, Ne) include (2, 3), (2, 4), (2, 5), (2, 6), (3, 2), (3, 4), (3, 5), (3, 6), (4, 2), (4, 3), (4, 5), (4, 6), (5, 2), (5, 3), (5, 4), (5, 6), (6, 2), (6, 3), (6, 4), and (6, 5).

In light of dimple effect, preferably, the pole vicinity region 30 has a sufficient area, and the equator vicinity region 32 has a sufficient area. In light of area of the equator vicinity region 32, each of the latitudes of the first latitude line 24 and the second latitude line 26 is preferably equal to or greater than 20° and more preferably equal to or greater than 25°. In light of area of the pole vicinity region 30, each of the latitudes of the first latitude line 24 and the second latitude line 26 is preferably equal to or less than 40° and more preferably equal to or less than 35°. The first latitude line 24 can be arbitrarily selected from among innumerable latitude lines. The second latitude line 26 can be also arbitrarily selected from among innumerable latitude lines. The mid latitude line 28 can be also arbitrarily selected from among innumerable latitude lines.

In light of contribution of the pole vicinity region 30 to the dimple effect, the ratio of the number of the dimples 20 that exist in the pole vicinity region 30 to the number of the dimples 20 that exist in the hemisphere is preferably equal to or greater than 20% and more preferably equal to or greater than 30%. This ratio is preferably equal to or less than 70%.

In light of contribution of the equator vicinity region 32 to the dimple effect, the ratio of the number of the dimples 20 that exist in the equator vicinity region 32 to the number of the dimples 20 that exist in the hemisphere is preferably equal to or greater than 20% and more preferably equal to or greater than 30%. This ratio is preferably equal to or less than 70%.

If the pole vicinity region 30 is adjacent to the equator vicinity region 32 across the boundary line, due to the difference in number of units, the dimples 20 cannot be arranged densely in the vicinity of this boundary line. In this case, a large land 22 exists in the vicinity of the boundary line. This large land 22 impairs the dimple effect. In the golf ball 14 according to the present invention, the mid region 34 exists between the pole vicinity region 30 and the equator vicinity region 32. The mid region 34 alleviates the difference between the characteristic of the pole vicinity region 30 and the characteristic of the equator vicinity region 32. The mid region 34 suppresses uneven location of the dimples 20 in the vicinity of the first latitude line 24 and also suppresses uneven location of the dimples 20 in the vicinity of the second latitude line 26. In the golf ball 14 having the mid region 34, a dimple pattern that does not have a large land 22 can be achieved. In the golf ball 14, a superior dimple effect is achieved. The golf ball 14 has excellent flight performance.

As described above, the number Nm of the dimples 20 included in the mid region 34 is 24. On the other hand, the number Np of the units Up of the pole vicinity region 30 is 4. The number Nm is a multiple of the number Np. In the golf ball 14, uneven location of the dimples 20 can be suppressed in the vicinity of the first latitude line 24. The number Ne of the units Ue of the equator vicinity region 32 is 6. The number Nm is a multiple of the number Ne. In the golf ball 14, uneven location of the dimples 20 can be suppressed in the vicinity of the second latitude line 26.

Preferably, the number Nm is a common multiple of the number Np and the number Ne. In the golf ball 14 with the number Nm being this common multiple, the mid region 34 can be divided into units the number of which is the number Np, and can be also divided into units the number of which is the number Ne.

The number Np of the units Up of the pole vicinity region 30 is preferably equal to or greater than 3. In the golf ball 14 with the number Np being 3 or greater, the area of each unit Up is not excessively large. The golf ball 14 has excellent aerodynamic symmetry. The number Np is preferably equal to or less than 6. In the golf ball 14 with the number Np being 6 or less, a superior dimple effect can be achieved.

The number Ne of the units Ue of the equator vicinity region 32 is preferably equal to or greater than 3. In the golf ball 14 with the number Ne being 3 or greater, the area of each unit Ue is not excessively large. The golf ball 14 has excellent aerodynamic symmetry. The number Ne is preferably equal to or less than 6. In the golf ball 14 with the number Ne being 6 or less, a superior dimple effect can be achieved.

Preferable combinations of the number Np, the number Ne, and the number Nm are shown in the following Table 1.

TABLE 1 Np Ne Nm 2 3 18 2 3 24 2 3 30 2 3 36 2 3 42 2 3 48 2 4 20 2 4 24 2 4 28 2 4 32 2 4 36 2 4 40 2 4 44 2 4 48 2 5 20 2 5 30 2 5 40 2 6 18 2 6 24 2 6 30 2 6 36 2 6 42 2 6 48 3 2 18 3 2 24 3 2 30 3 2 36 3 2 42 3 2 48 3 4 24 3 4 36 3 4 48 3 5 30 3 5 45 3 6 18 3 6 24 3 6 30 3 6 36 3 6 42 3 6 48 4 2 20 4 2 24 4 2 28 4 2 32 4 2 36 4 2 40 4 2 44 4 2 48 4 3 24 4 3 36 4 3 48 4 5 20 4 5 40 4 6 24 4 6 36 4 6 48 5 2 20 5 2 30 5 2 40 5 3 30 5 3 45 5 4 20 5 4 40 5 6 30 6 2 18 6 2 24 6 2 30 6 2 36 6 2 42 6 2 48 6 3 18 6 3 24 6 3 30 6 3 36 6 3 42 6 3 48 6 4 24 6 4 36 6 4 48 6 5 30

The number of the dimples 20 that are adjacent to the first latitude line 24 and included in the pole vicinity region 30 preferably agrees with the number of the dimples 20 that are arranged along the mid latitude line 28. Due to this agreement, the dimples 20 that exist in the pole vicinity region 30 and the dimples 20 that exist in the mid region 34 can be alternately arranged across the first latitude line 24. Due to this alternate arrangement, uneven location of the dimples 20 is suppressed. In the dimple pattern shown in FIGS. 2 to 5, the number of the dimples 20 that are adjacent to the first latitude line 24 and included in the pole vicinity region 30 is 24. In this pattern, the number of the dimples 20 that are arranged along the mid latitude line 28 is 24. Both of the numbers agree with each other.

The number of the dimples 20 that are adjacent to the second latitude line 26 and included in the equator vicinity region 32 preferably agrees with the number of the dimples 20 that are arranged along the mid latitude line 28. Due to this agreement, the dimples 20 that exist in the equator vicinity region 32 and the dimples 20 that exist in the mid region 34 can be alternately arranged across the second latitude line 26. Due to this alternate arrangement, uneven location of the dimples 20 is suppressed. In the dimple pattern shown in FIGS. 2 to 5, the number of the dimples 20 that are adjacent to the second latitude line 26 and included in the equator vicinity region 32 is 24. In this pattern, the number of the dimples 20 that are arranged along the mid latitude line 28 is 24. Both of the numbers agree with each other.

In light of suppression of uneven location of the dimples 20, the dimples 20 included in the mid region 34 preferably have the same diameter. In light of suppression of uneven location of the dimples 20, these dimples 20 are preferably arranged along the mid latitude line 28 at regular intervals.

The number Nm of the dimples 20 in the mid region 34 is preferably equal to or greater than 18. In the golf ball 14 with the number Nm being 18 or greater, each dimple 20 is not excessively large. In the golf ball 14, the area of the land 22 can be suppressed. In this respect, the number Nm is more preferably equal to or greater than 20 and particularly preferably equal to or greater than 24. When the dimples 20 included in the mid region 34 have the same diameter and are arranged at regular intervals, the central angle between two adjacent dimples 20 is preferably equal to or less than 20°, more preferably equal to or less than 18°, and particularly preferably equal to or less than 15°.

The number Nm of the dimples 20 in the mid region 34 is preferably equal to or less than 48. In the golf ball 14 with the number Nm being 48 or less, each dimple 20 is sufficiently large. Due to these dimples 20, a superior dimple effect is achieved. In this respect, the number Nm is more preferably equal to or less than 45 and particularly preferably equal to or less than 42. When the dimples 20 included in the mid region 34 have the same diameter and are arranged at regular intervals, the central angle between two adjacent dimples 20 is preferably equal to or greater than 7.5°, more preferably equal to or greater than 8.0°, and particularly preferably equal to or greater than 8.5°. The central angle is preferably equal to or less than 20°.

The latitude of the mid latitude line 28 is preferably equal to or greater than 20° and equal to or less than 40°. By setting the latitude to be 20° or greater, the equator vicinity region 32 has a sufficient area. By setting the latitude to be 40° or less, the pole vicinity region 30 has a sufficient area. In the golf ball 14 with the latitude being 20° or greater and 40° or less, air flow is sufficiently disturbed. In this respect, the latitude is particularly preferably equal to or greater than 25°. The latitude is particularly preferably equal to or less than 35°. Ideally, the latitude is 30°. In the golf ball 14 with the latitude being 30°, the area of the region that exists in the surface of the phantom sphere and between the mid latitude line 28 and the equatorial line Eq agrees with the area of the region that exists in the surface of the phantom sphere and between the mid latitude line 28 and the pole P.

In light of aerodynamic symmetry, the dimple pattern of the northern hemisphere N is preferably equivalent to the dimple pattern of the southern hemisphere S. When a pattern that is symmetrical to the dimple pattern of the northern hemisphere N about the plane that includes the equatorial line Eq substantially overlaps the dimple pattern of the southern hemisphere S, these patterns are determined to be equivalent to each other. In addition, when the pattern that is symmetrical to the dimple pattern of the northern hemisphere N about the plane that includes the equatorial line Eq is rotated about the pole P and the rotated pattern substantially overlaps the dimple pattern of the southern hemisphere S, these patterns are determined to be equivalent to each other.

Some dimples 20 may intersect the equatorial line Eq. The dimples 20 whose centers are located in the northern hemisphere N belong to the northern hemisphere N. The dimples 20 whose centers are located in the southern hemisphere S belong to the southern hemisphere S. The dimples 20 whose latitudes are zero belong to the northern hemisphere N and the southern hemisphere S.

From the standpoint that a sufficient dimple effect is achieved, the total number of the dimples 20 is preferably equal to or greater than 200 and particularly preferably equal to or greater than 260. From the standpoint that each dimple 20 can have a sufficient diameter, the total number is preferably equal to or less than 600, more preferably equal to or less than 500, and particularly preferably equal to or less than 400.

FIG. 6 is a partially enlarged cross-sectional view of the golf ball 14 in FIG. 1. FIG. 6 shows a cross section along a plane passing through the deepest part of the dimple 20 and the center of the golf ball 14. In FIG. 6, the top-to-bottom direction is the depth direction of the dimple 20. What is indicated by a chain double-dashed line 40 in FIG. 6 is the surface of the phantom sphere 40. The dimple 20 is recessed from the surface of the phantom sphere 40. The land 22 agrees with the surface of the phantom sphere 40.

In FIG. 6, what is indicated by a double ended arrow Di is the diameter of the dimple 20. The diameter Di is the distance between two tangent points Ed appearing on a tangent line T that is drawn tangent to the far opposite ends of the dimple 20. Each tangent point Ed is also the edge of the dimple 20. The edge Ed defines the contour of the dimple 20. The diameter Di is preferably equal to or greater than 2.00 mm and equal to or less than 6.00 mm. By setting the diameter Di to be 2.00 mm or greater, a superior dimple effect is achieved. In this respect, the diameter Di is more preferably equal to or greater than 2.20 mm and particularly preferably equal to or greater than 2.40 mm. By setting the diameter Di to be 6.00 mm or less, a fundamental feature of the golf ball 14 being substantially a sphere is maintained. In this respect, the diameter Di is more preferably equal to or less than 5.80 mm and particularly preferably equal to or less than 5.60 mm.

The area s of the dimple 20 is the area of a region surrounded by the contour line when the center of the golf ball 14 is viewed at infinity. In the case of a circular dimple 20, the area s is calculated by the following formula.

s=(Di/2)²*π

In the golf ball 14 shown in FIGS. 1 to 6, the area of the dimple A is 19.63 mm²; the area of the dimple B is 18.10 mm²; the area of the dimple C is 17.35 mm²; the area of the dimple D is 15.20 mm²; the area of the dimple E is 12.57 mm²; the area of the dimple F is 10.18 mm²; and the area of the dimple G is 7.07 mm².

In the present invention, the ratio of the sum of the areas s of all the dimples 20 to the surface area of the phantom sphere 40 is referred to as an occupation ratio. From the standpoint that a sufficient dimple effect is achieved, the occupation ratio is preferably equal to or greater than 60%, more preferably equal to or greater than 65%, and particularly preferably equal to or greater than 70%. The occupation ratio is preferably equal to or less than 88%. In the golf ball 14 shown in FIGS. 2 to 6, the total area of the dimples 20 is 4442.8 mm². The surface area of the phantom sphere 40 of the golf ball 14 is 5728.0 mm², and thus the occupation ratio is 77.6%.

In the present invention, the term “dimple volume” means the volume of a part surrounded by the surface of the dimple 20 and a plane that includes the contour of the dimple 20. In light of suppression of rising of the golf ball 14 during flight, the total volume of all the dimples is preferably equal to or greater than 250 mm³, more preferably equal to or greater than 260 mm³, and particularly preferably equal to or greater than 270 mm³. In light of suppression of dropping of the golf ball 14 during flight, the total volume is preferably equal to or less than 400 mm³, more preferably equal to or less than 390 mm³, and particularly preferably equal to or less than 380 mm³.

In light of suppression of rising of the golf ball 14 during flight, the depth of the dimple 20 is preferably equal to or greater than 0.05 mm, more preferably equal to or greater than 0.08 mm, and particularly preferably equal to or greater than 0.10 mm. In light of suppression of dropping of the golf ball 14 during flight, the depth of the dimple 20 is preferably equal to or less than 0.60 mm, more preferably equal to or less than 0.45 mm, and particularly preferably equal to or less than 0.40 mm. The depth is the distance between the tangent line T and the deepest part of the dimple 20.

EXAMPLES Example

A rubber composition was obtained by kneading 100 parts by weight of a polybutadiene (trade name “BR-730”, available from JSR Corporation), 30 parts by weight of zinc diacrylate, 6 parts by weight of zinc oxide, 10 parts by weight of barium sulfate, 0.5 part by weight of diphenyl disulfide, and 0.5 part by weight of dicumyl peroxide. This rubber composition was placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 170° C. for 18 minutes to obtain a core with a diameter of 39.7 mm. Meanwhile, a resin composition was obtained by kneading 50 parts by weight of an ionomer resin (trade name “Himilan 1605”, available from Du Pont-MITSUI POLYCHEMICALS Co., LTD.), 50 parts by weight of another ionomer resin (trade name “Himilan 1706”, available from Du Pont-MITSUI POLYCHEMICALS Co., LTD.), and 3 parts by weight of titanium dioxide. The above core was placed into a final mold having numerous pimples on its inside face, followed by injection of the above resin composition around the core by injection molding to form a cover with a thickness of 1.5 mm. Numerous dimples having a shape that was the inverted shape of the pimples were formed on the cover. A clear paint including a two-component curing type polyurethane as a base material was applied to this cover to obtain a golf ball of Example having a diameter of 42.7 mm and a weight of about 45.4 g. The golf ball has a PGA compression of about 85. The golf ball has the dimple pattern shown in FIGS. 2 to 5. The detailed specifications of the dimples are shown in the following Table 2.

Comparative Example 1

A golf ball of Comparative Example 1 was obtained in a similar manner as Example, except the final mold was changed so as to form dimples whose specifications are shown in the following Table 2. FIG. 7 is a front view of this golf ball, and FIG. 8 is a plan view of this golf ball. Each of the northern hemisphere and the southern hemisphere of this golf ball has a pole vicinity region, an equator vicinity region, and a mid region. Each pole vicinity region consists of four units Up that are rotationally symmetrical to each other about the pole P. Each equator vicinity region consists of four units Ue that are rotationally symmetrical to each other about the pole P. Each mid region has 24 dimples. These dimples are arranged along a latitude line with a latitude of 30°.

Comparative Example 2

A golf ball of Comparative Example 2 was obtained in a similar manner as Example, except the final mold was changed so as to form dimples whose specifications are shown in the following Table 3. FIG. 9 is a front view of this golf ball, and FIG. 10 is a plan view of this golf ball. Each of the northern hemisphere and the southern hemisphere of this golf ball has a pole vicinity region, an equator vicinity region, and a mid region. Each pole vicinity region consists of six units Up that are rotationally symmetrical to each other about the pole P. Each equator vicinity region consists of six units Ue that are rotationally symmetrical to each other about the pole P. Each mid region has 24 dimples. These dimples are arranged along a latitude line with a latitude of 30°.

Comparative Example 3

A golf ball of Comparative Example 3 was obtained in a similar manner as Example, except the final mold was changed so as to form dimples whose specifications are shown in the following Table 3. FIG. 11 is a front view of this golf ball, and FIGS. 12 to 14 are plan views of this golf ball. Each of the northern hemisphere and the southern hemisphere of this golf ball has a pole vicinity region, an equator vicinity region, and a coordination region. Each pole vicinity region consists of five units Up that are rotationally symmetrical to each other about the pole P. Each equator vicinity region consists of six units Ue that are rotationally symmetrical to each other about the pole P. This golf ball is disclosed in US2007/149321 (JP2007-175267).

TABLE 2 Specifications of Dimples Number Pole vicinity Equator vicinity Coordination Diameter Depth Radius Volume Type region region Mid region region (mm) (mm) (mm) (mm³) Example A 16 36 0 — 5.00 0.145 21.62 1.425 B 8 36 0 — 4.80 0.145 19.93 1.314 C 0 0 48 — 4.70 0.145 19.12 1.259 D 32 24 0 — 4.40 0.145 16.76 1.104 E 40 0 0 — 4.00 0.145 13.87 0.913 F 32 0 0 — 3.60 0.145 11.24 0.740 G 16 0 0 — 3.00 0.145 7.83 0.514 Comparative A 16 40 0 — 5.00 0.145 21.62 1.425 Example 1 B 8 32 0 — 4.80 0.145 19.93 1.314 C 0 0 48 — 4.70 0.145 19.12 1.259 D 32 24 0 — 4.40 0.145 16.76 1.104 E 40 0 0 — 4.00 0.145 13.87 0.913 F 32 0 0 — 3.60 0.145 11.24 0.740 G 16 0 0 — 3.00 0.145 7.83 0.514

TABLE 3 Specifications of Dimples Number Pole vicinity Equator vicinity Coordination Diameter Depth Radius Volume Type region region Mid region region (mm) (mm) (mm) (mm³) Comparative A 24 36 0 — 5.00 0.145 21.62 1.425 Example 2 B 0 36 0 — 4.80 0.145 19.93 1.314 C 0 0 48  — 4.70 0.145 19.12 1.259 D 36 24 0 — 4.40 0.145 16.76 1.104 E 48 0 0 — 4.00 0.145 13.87 0.913 F 0 0 0 — 3.60 0.145 11.24 0.740 G 36 0 0 — 3.00 0.145 7.83 0.514 Comparative A 60 12 — 8 4.55 0.138 18.82 1.123 Example 3 B 20 60 — 0 4.45 0.138 18.01 1.075 C 0 60 — 0 4.25 0.138 16.43 0.980 D 0 24 — 16 4.10 0.138 15.30 0.912 E 20 24 — 12 3.85 0.138 13.50 0.805 F 2 12 — 0 3.00 0.138 8.22 0.489

[Flight Distance Test]

A driver with a titanium head (Trade name “XXIO”, available from Sumitomo Rubber Industries, Ltd., shaft hardness: X, loft angle: 9°) was attached to a swing machine available from True Temper Co. A golf ball was hit under the conditions of: a head speed of 49 m/sec; a launch angle of about 11°; and a backspin rotation rate of about 3000 rpm, and the distance from the launch point to the stop point was measured. At the test, the weather was almost windless. The average value of 20 measurements is shown in the following Table 4.

TABLE 4 Results of Evaluation Compara. Compara. Compara. Example Example 1 Example 2 Example 3 Total number 288 288 288 330 Total volume (mm³) 322.6 323.0 321.8 323.0 Occupation ratio (%) 77.6 77.7 77.4 81.6 Pole vicinity Rotational symmetry angle (degree) 90 90 60 72 region Number of units Np 4 4 6 5 Equator vicinity Rotational symmetry angle (degree) 60 90 60 60 region Number of units Ne 6 4 6 6 Mid region Pattern Regular Regular Regular — intervals intervals intervals Latitude of mid latitude line 30 30 30 — Dimple number 24 24 24 — Coordination Pattern — — — Line region symmetry Flight distance (m) 242.1 238.8 239.2 240.4

As shown in Table 4, the golf ball of Example has excellent flight performance. From the results of evaluation, advantages of the present invention are clear.

The dimple pattern described above is applicable to a one-piece golf ball, a multi-piece golf ball, and a thread-wound golf ball, in addition to a two-piece golf ball. The above description is merely for illustrative examples, and various modifications can be made without departing from the principles of the present invention. 

1. A golf ball having, in a surface thereof, a northern hemisphere and a southern hemisphere each of which has a pole vicinity region, an equator vicinity region, and a mid region located between the pole vicinity region and the equator vicinity region, wherein each of the pole vicinity region, the equator vicinity region, and the mid region has a large number of dimples, a dimple pattern of the pole vicinity region includes a plurality of units that are rotationally symmetrical to each other about a pole, a dimple pattern of the equator vicinity region includes a plurality of units that are rotationally symmetrical to each other about the pole, the number Np of the units of the pole vicinity region is different from the number Ne of the units of the equator vicinity region, and the dimples included in the mid region are arranged substantially along a latitude line.
 2. The golf ball according to claim 1, wherein the latitude line has a latitude of 20° or greater and 40° or less.
 3. The golf ball according to claim 2, wherein the latitude of the latitude line is substantially 30°.
 4. The golf ball according to claim 1, wherein the number Np is equal to or greater than 3 and equal to or less than 6, and the number Ne is equal to or greater than 3 and equal to or less than
 6. 5. The golf ball according to claim 1, wherein the number Nm of the dimples in the mid region is equal to or greater than 18 and equal to or less than
 48. 6. The golf ball according to claim 1, wherein the number Nm of the dimples in the mid region is a common multiple of the number Np and the number Ne.
 7. The golf ball according to claim 1, wherein the dimples included in the mid region have the same diameter, and these dimples are arranged along the latitude line at regular intervals.
 8. The golf ball according to claim 7, wherein a central angle between dimples adjacent to each other is equal to or greater than 7.5° and equal to or less than 20°.
 9. The golf ball according to claim 1, wherein the number of dimples that are adjacent to a boundary line between the pole vicinity region and the mid region and included in the pole vicinity region is equal to the number of the dimples that are arranged along the latitude line.
 10. The golf ball according to claim 1, wherein the number of dimples that are adjacent to a boundary line between the equator vicinity region and the mid region and included in the equator vicinity region is equal to the number of the dimples that are arranged along the latitude line.
 11. The golf ball according to claim 1, wherein a ratio of the number of the dimples that exist in the pole vicinity region to the number of the dimples that exist in each hemisphere is equal to or greater than 20% and equal to or less than 70%.
 12. The golf ball according to claim 1, wherein a ratio of the number of the dimples that exist in the equator vicinity region to the number of the dimples that exist in each hemisphere is equal to or greater than 20% and equal to or less than 70%.
 13. The golf ball according to claim 1, wherein a dimple pattern of the northern hemisphere is equivalent to a dimple pattern of the southern hemisphere.
 14. The golf ball according to claim 1, wherein the total number of the dimples is equal to or greater than 200 and equal to or less than
 600. 15. The golf ball according to claim 1, wherein each dimple has a diameter of 2.00 mm or greater and 6.00 mm or less.
 16. The golf ball according to claim 1, wherein a ratio of the sum of areas of all the dimples to a surface area of a phantom sphere is equal to or greater than 60% and equal to or less than 88%.
 17. The golf ball according to claim 1, wherein the total volume of the dimples is equal to or greater than 250 mm³ and equal to or less than 400 mm³.
 18. The golf ball according to claim 1, wherein each dimple has a depth of 0.05 mm or greater and 0.60 mm or less. 